The development of a practical, lightweight internal combustion engine of the compression ignition type has been a goal of engine designers for many decades. Great strides have been made toward this goal. However, no engine design has heretofore been disclosed which is sufficiently superior, in a practical sense, to displace the spark ignition internal combustion engine as the preferred choice in high volume applications such as for powering automobiles. In an attempt to provide the increased strength required in a compression ignition engine without adding significantly to the cost and weight of the engine, it has been proposed to form the engine head and cylinder block as a one-piece integral unit such as illustrated in U.S. Pat. Nos. 3,674,000 and 3,691,914. Engine designs of the type illustrated in these patents obviously have the desirable effect of eliminating the requirement for a high temperature, high pressure head gasket seal. In addition to reducing cost, elimination of the head gasket also simplifies the head design by eliminating the need for head bolts and corresponding head bolt bosses.
While achieving the advantages noted above, previously disclosed integral head and cylinder block designs have suffered from several significant drawbacks. For example, it has generally been considered good practice in a liquid cooled engine to extend the cooling jacket over substantially the entire axial length of the cylinder cavity. When formed to accommodate this requirement, an integral head and cylinder block for a liquid cooled engine becomes quite heavy and bulky. Obviously, significant assembly and maintenance problems result when such a substantial portion of the entire engine assembly is formed as a single unit. Moreover, the depth of the cylinder cavities imposes manufacturing difficulties particularly with respect to forming the valve seats at the base of each cavity. Integral head and block units are also susceptible to cracks at the juncture of the cylinder head bottom and the inner wall of the cylinder cavity by reason of the high combustion pressure and thermal stresses existant at this location as discussed in U.S. Pat. No. 3,691,914. Further problems result from the use of substantially full length liquid cooling jackets since such jackets require a relatively complicated, high volume coolant system and add to the overall size and weight of the integral head and block.
Still another complication which has tended to discourage the use of integral head and block designs has been the difficulty associated with the use of removable liners within the cylinder cavities. It has long been recognized that removable cylinder liners provide significant cost and performance advantages in internal combustion engines by permitting, for example, the engine to be overhauled simply by replacement of the cylinder liners without requiring the use of oversized pistons or rings. Removable liners are generally categorized as either "dry" or "wet". A "dry" liner is one from which the heat of combustion is removed without bringing the liquid engine coolant into direct contact with the liner (illustrated, for example, in U.S. Pat. Nos. 1,488,272 and 3,521,613). A "wet" liner, on the other hand, is one from which heat is removed by direct contact with the coolant. See for example U.S. Pat. No. 3,942,807. Wet liners are considered to be more desirable since the cylinder block can be simplified in design and since cooling efficiency is increased by direct contact of the coolant with the liner. However, wet liners present additional sealing problems over dry liners since wet liners must be sealed against coolant as well as combustion gas leakage. When employed in combination with an integral head and cylinder block, wet liners create further coolant sealing problems requiring close tolerances especially in designs employing substantially full length coolant jackets such as illustrated in U.S. Pat. Nos. 1,716,256, 2,170,443 and 2,125,106 and in British Patent No. 522,741 accepted June 26, 1940.
Cylinder liners may be further categorized in accordance with the manner by which the liner is retained within the cylinder cavity. By far the most common approach in conventional two piece head and cylinder engine designs is to provide a top flange adopted to be compressively held between the top of the engine block and the removable head such as disclosed in U.S. Pat. No. 3,463,056. Where the head and block are formed integrally, the conventional retaining flange must obviously be moved to a different point on the exterior of the cylinder liner such as illustrated in U.S. Pat. No. 1,488,272, wherein an integral head and partial cylinder block is disclosed in combination with a dry liner having a retaining flange positioned at the juncture between the upper and lower sections of the block. This type of liner is known as a "midstop" liner. Another approach has been to remove the flange altogether and trap the liner between its ends as illustrated in U.S. Pat. No. 3,046,953. Liners may also be attached at their lower ends with sufficient axial clearance being provided at their upper ends to permit axial thermal expansion without imposing compressive stress on the liner such as illustrated in U.S. Pat. No. 1,410,752. Still another approach has been to abandon the conventional retaining flange in favor of a screw threaded connection between the liner and engine block as illustrated in U.S. Pat. No. 1,716,256. The problems associated with the machining of screw threads within the upper portion of each cylinder cavity of an integral head and substantially full length cylinder block as shown in this patent are readily apparent.
Since wet liners are normally employed in circumstances where a full length coolant jacket is used, it is unusual for the retaining flange of a wet liner to be positioned intermediate the ends of the liner. Such a concept is disclosed, however, in U.S. Pat. No. 3,568,573 wherein the liner is supported by a shoulder located approximately at the midsection of the liner while the coolant jacket extends downwardly (toward the crankcase) of this shoulder thereby forming a "dry" liner portion downwardly of the shoulder and a "wet" liner portion upwardly of the shoulder. French Pat. No. 1,116,882 discloses a similar arrangement. In those few known engine designs employing a midstop "wet" liner combined with a coolant system in which all heat transfer with the coolant occurs upwardly of the midstop, such as illustrated in U.S. Pat. Nos. 1,607,265 and 3,315,573, the midstop is positioned within the vicinity of the lower limit of travel of the top of the piston. Thus, the midstop is positioned no closer to the outer end of the liner than approximately 50 percent of the total axial length of the liner.
In modern turbocharged engines, it is considered highly desirable to maintain the maximum possible amount of usable energy in the exhaust gases for use in operating the turbocharger. In spite of this recognition, the axial length of the coolant jackets in wet linered turbocharged engines has not heretofore been reduced below 50% of the total axial length of the liner due to the apparent belief that excessive engine temperatures would result. Prior limited cooling concepts have been suggested, such as disclosed in British Pat. No. 1,479,139, but such concepts have not been thought to be applicable to wet linered turbocharged engines.
In addition to the difficulties associated with the use of integral head and block designs and with the use of wet liners, internal combustion engines particularly of the compression ignition type often produce excessive noise unless costly sound baffling techniques are employed. Heretofore, no integral head and block design employing a wet liner has been disclosed which is characterized simultaneously by low operational noise generation.